Gas drilling soil sampling

ABSTRACT

The concentration with location at which a mobile reservoir fluid is contained within subsurface earth formations is measured by gas drilling a borehole into the earth formations while circulating a gaseous drilling fluid that is initially substantially free of the mobile reservoir fluid and measuring the concentration of the reservoir fluid in the earth formations by measuring the difference in its concentration in equivalent portions of the drilling fluid that enters and leaves the borehole.

llite tes Turner et al.

* atet [54] GAS DRILLENG SOHJL SAMPLING [72] Inventors: James B. Turner,4709 Tonawanda; Harold 1... Wise, 4522 Hummingbird, both of Houston,Tex. 77035 [22] Filed: May 20, 1970 [21] Appl.N0.: 39,677

[52] US. Cl ..73/153 [51] llnt. Cl ..E2lb 49/00 [58] Field ofSearch..73/153, 152

[56] References Cited UNITED STATES PATENTS 2,214,674 9/1 940 Hayward..73/1 53 Feb. 29, 1972 2,740,292 4/1956 Sewell ..73/153 3,031,5714/1962 Fearon.... .....73/153X 3,514,996 6/1970 Coustau ..73/l53 PrimaryExaminerJerry W. Myracle Attorney-Harold W. Coryell and J. H. McCarthy[57] ABSTRACT The concentration with location at which a mobilereservoir fluid is contained within subsurface earth formations ismeasured by gas drilling a borehole into the earth formations whilecirculating a gaseous drilling fluid that is initially substantiallyfree of the mobile reservoir fluid and measuring the concentration ofthe reservoir fluid in the earth formations by measuring the differencein its concentration in equivalent portions of the drilling fluid thatenters and leaves the borehole.

9 Claims, 2 Drawing Figures United States Patent I [151 3,645,131 Turneret a1. 5] Feb. 29, 11972 [54] GAS DRILLING SOIL SAMPLING 2,740,2924/1956 Sewell ..73/153 [72] Inventors: James B. Turner, 4709 Tonawanda;303157l 4/1962 Feamnm X 3,514,996 6/1970 Coustau ..73/l53 Harold L.Wise, 4522 Hummingbird, both of Houston 77035 Primary Examiner-Jerry W.Myracle 22 Filed; May 20 1970 Attorney-Harold W. Coryell and J. H.McCarthy 1 1 pp 39,677 [57] ABSTRACT The concentration with location atwhich a mobile reservoir [52] US. Cl ..73/l53 fluid is contained withinsubsurface earth formations is mea- [5 1] Int. Cl ,E21b 49/00 sured bygas drilling a borehole into the earth formations while 58 Field ofSearch ..73/153, 152 circulating a gaseous drilling fluid that isinitially Substantially free of the mobile reservoir fluid and measuringthe concen- [56] References Cited tration of the reservoir fluid in theearth formations by measuring the difference in its concentration inequivalent por- UNITED STATES PATENTS tions of the drilling fluid thatenters and leaves the borehole 2,214,674 9/ 1940 Hayward ..73/153 9Claims, 2 Drawing Figures PATENTEDFEB29 1912 3.645.131

INVENTORS.

J. B. TURNER H. L. WISE GAS DRILLING SOIL SAMPLING BACKGROUND OF THEINVENTION The invention relates to an exploration process for locating asubterranean reservoir. It is particularly useful for locating apetroleum reservoir under dry land.

A mobile reservoir fluid, such as a light hydrocarbon or an inorganicgas, tends to escape from a reservoir and migrate up toward the surfaceof the earth. The migrating fluid flows through permeable earthformations containing interconnected pores or fractures that arenormally filled with at least one natural fluid, such as water or air.The migrating mobile fluid tends to rise above and/or be dispersed inthe fluid in the rock, due to effects such as gravity segregation and/ordiffusion. Some of the migrating fluid is adsorbed on the surfaces ofthe rocks.

Previously proposed procedures for locating petroleum reservoirs measurethe concentrations with location of the hydrocarbons that are containedin core samples, those contained in bit cuttings, those that becomeentrained in circulating liquid drilling fluids or muds, those that aredissolved or entrained in the fluids which flow into a borehole when thepressure within the borehole is reduced, etc. The concentrations atwhich the hydrocarbons are present in relatively shallow earthformations tend to be very small, generally less than one part permillion. Because of this, such previously proposed geochemicalexploration procedures have tended to require costly operations, such asthe careful collecting and preserving and analyzing of whole samples ofthe earth forma tions; or have tended to provide measurements that aredifficult to correlate with respect to each other or with respect toother information, such as seismic information, relating to the regionbeing explored.

SUMMARY OF THE INVENTION In accordance with the present invention, earthformations are sampled by gas drilling boreholes into them whilecirculating a gaseous drilling fluid that is initially substantiallyfree of a selected mobile reservoir fluid. The concentration of themobile reservoir fluid in the earth formations around the borehole ismeasured by measuring the difference in its concentration in equivalentportions of the drilling fluid as the drilling fluid enters and leavesthe borehole. Such measurements indicate the concentration of the mobilereservoir fluid with areal location and/or depth within the earthformations.

DESCRIPTION OF THE DRAWING FIG. 1 is a schematic illustration of asystem for practicing the invention.

FIG. 2 shows a multiple-port valve of the system of FIG. 1 with theports in a different operational position.

DESCRIPTION OF THE INVENTION FIG. 1 shows a gas drilling systemcomprising a rig structure 1, a drill string assembly 2, agaseous-drilling fluid input line 3 (which is connected to a compressoror blower, not shown) a bit-cuttings separator 4, and a gas dischargesample line 5. A chromatograph 6 is arranged to measure theconcentration of a selected mobile reservoir fluid in the inflowinggaseous drilling fluid before it has been circulated into borehole 7. Aliquids and solids separator 8 is connected to receive and treat aportion of the gas being discharged from the bit-cuttings separator 4.The gas treated by separator 8 is supplied to a manifold 9. Manifold 9preferably contains a filter means, such as a micropore dust filter,(not shown) for further cleaning the gas. A transfer pump 10 isconnected to displace a sample stream of gas from the manifold 9 througha drying means II and into a multiport valve 12. The valve 12, inposition shown, allows a sample stream of gas to flow through a sampletrap loop 13 and exit through port 14.

As shown in FIG. 2, the position of the ports in valve 12 can bearranged so that the fluid in trap loop 13 is displaced throughchromatograph l5 and discharged through port 16. The displacement of thefluid from trap loop 13 is preferably effected by allowing an inflow ofclean gas from .a source 17 and outflow, ultimately through port 16, asindicated by the arrows. The pressure of the fluid displaced intochromatograph 15 is preferably regulated by a throttle valve [8 arrangedupstream of discharge port 16 to maintain a pressure between that of arelatively high pressure at clean air source 17 and atmosphericpressure.

In a preferred arrangement, check valve 19 is placed upstream frommultiport valve I2 to restrict backflow without significantly impedingforward flow. Pump 10 is preferably operated at substantiallyatmospheric pressure. If sample loop 13 is filled with clean gas at ahigher pressure when it is connected to the outflow from check valve 19,the higher pressure is dissipated by a purge through discharge port 14and the loop is refilled with undiluted sample gas at substantiallyatmospheric pressure.

Suitable chromatographs and chromatographic-measuring techniques areknow. Examples of such devices and procedures are contained in US. Pat.Nos. 2,918,579; 3,116,133;3,296,776 and 3,455,144.

In general, the gas drilling equipment used in the present invention cancomprise substantially any such system which has been freed of the fluidbeing sampled to an extent such that only insignificant amounts areimparted to the gaseous drilling fluid that is circulated through thedrilling system. In a preferred procedure the ensurance of this includesa hydrocarbon-removing treatment comprising contacting all portions ofthe drilling system that will be contacted by a circulating drillingfluid with a nonhydrocarbon solvent, such as an alcohol, ketone, ether,ester, or the like. All of the hydrocarbon lubricants are preferablyreplaced with nonhydrocarbon lubricants, such as the silicone oils andgreases that are commercially available from Dow Chemical Company underthe trademarks DC-200 (Oil) and DC-44 (Grease). In a preferredarrangement, the drilling fluid circulation is powered by a blowerhaving fan blades mounted within a compartment that is isolated from thehearing. The drilling fluid circulating means is preferably arranged tointake relatively clean air from a substantially contaminant-freelocation, such as the top of the drilling rig. The drilling fluidexhaust or blooey line" (not shown in the drawing) is preferablyextended to a location that is both relatively remote from and downwindof the intake location.

In practicing this invention the measurement of the concentration of theselected fluid (such as a hydrocarbon) in the circulating drillingfluid, can be made by means of substantially any measuring device whichis relatively sensitive and accurate with respect to concentrations ofless than about one part per million. A chromatograph comprising acombination of a chromatographic column, a flame ionization detector,and an electrometer is a preferred type of such a measuring device. Thesampling and analyzing of the drilling fluid before and after itscirculation into the borehole can be performed by means of one or moresuch measuring devices. It is desirable that, at substantially eachincrement of depth of the borehole, at least one measurement before andafter such circulation is made on the same portion (or on substantiallyequivalent portions) of the circulating gaseous drilling fluid. In thesystem shown in the drawing, for a given rate of drilling fluidcirculation, a portion of an inflowing gas on which a measurement ismade as the gas enters the drill string assembly 2 (by means ofchromatograph 6) will, after a determinable length of time, become thegas that is filling the trap loop 13 of valve 12. The gas in the traploop is isolated for measurement (by means of chromatograph l5) bychanging the post arrangement of valve 12.

In field operations utilizing chromatographic measurements, it has beenfound that samples of about It) cc. in volume are adequate, and suchmeasurements can readily be repeated as often as every 15 seconds. At atypical drilling rate of about 6 feet per minute such a sampling rateprovides a

1. In a process for mapping the concentration with location of a mobilereservoir fluid inclusive of at least one hydrocarbon in subsurfaceearth formations, the improvement which comprises: gas drilling aborehole into the subsurface earth formations while circulating gaseousdrilling fluid that is substantially free of hydrocarbon; measuring theconcentration of at least one hydrocarbon at selected repetitiveincrements of depth in equivalent portions of the circulating drillingfluid before and after those portions have circulated through theborehole; and measuring the difference between said before and afterconcentrations in order to measure the concentration of at least onehydrocarbon with depth within the earth formations encountered by theborehole.
 2. The process of claim 1 in which the drilling fluid is airthat enters an intake which is located in a position that is relativelyremote from and upwind relative to the location of the drilling fluidexhaust.
 3. The process of claim 2 in which the measurements includemeasurements of at least one inorganic gas.
 4. The process of claim 2 inwhich the drilling fluid circulation is maintained at substantially thesame relatively high rate while the portions of the drilling fluid onwhich said concentration measurements are made are flowing through theborehole.
 5. The process of claim 1 in which: a plurality of boreholesare drilled in locations which are adapted for use in a pattern ofseismic source and receiver locations; and said boreholes are used forthe implanting of equipment used in a seismic exploration of thesubsurface earth formations.
 6. The process of claim 1 in whichmeasurements are made of the concentration with depth of the mobilereservoir fluid.
 7. The process of claim 1 in which: said borehole islogged with respect to the magnitude with depth of a rock-typeresponsive property; measurements are made of the depths of magnitudesof said logged property which are characteristic of a selected type ofearth formation in order to identify the depths of individual earthformations; and measurements are made of the concentration of the mobilereservoir Fluid in at least one selected type of individual earthformation.
 8. The process of claim 1 in which measurements are made ofthe maximum concentration of the mobile reservoir fluid within aselected interval of depth.
 9. The process of claim 1 in which theequipment used for gas drilling the borehole is pretreated bycirculating through it a fluid that is chemically distinct from butmiscible with said mobile reservoir fluid until substantially no mobilereservoir fluid is entrained in a gaseous fluid that is circulatedthrough the drilling system.